It’s useful to know if you’re changing jobs or inline for a pay rise, at it will help you see how much you are likely to be taking home in your pay packet each month.

Also, if you’re a student, it will give you an idea of the repayment threshold for your student loan (although I think things might have changed since my days as a student, as the amount you have to earn before paying back your loan is significantly higher than it appears to be now).